"I was looking at options. One was to go to Indycar in America. I heard there were new cars coming to Japan and decided to go and test them in December. I was fastest in testing in December in Fuji and then the team invited me again in January and it went really well," said the ex-Formula One driver, who is being supported by Tata Group.

"The cars are really fast so I decided on this championship. There are several (former) F1 drivers driving here so it's a very tough competition. It will be quite a challenge," he told reporters here.

"I am comfortable in the car. We would like to have had more testing in dry conditions. But it wasn't to be. On the last day of testing in Fuji, I was fourth fastest which is not so bad. It's going to be very competitive and challenging," he said.

Karthikeyan, who will drive for Team Impul Hoshino Racing, said with new cars this year the format should be on par with the glamorous Formula One in terms of speed and times clocked.

"I was pleasantly surprised that we have a new car this year, the Dallara SF 14, 2.0 litre engine. Compared to Formula One last year, we were three seconds off in similar tyres.

With F1 slowing down this year, we should be on par in terms of times. "It is going to be really fast with the format being the same as F1 with a pit stop and a luxury of a fuel stop as well. Quite a lot of strategies will come in to place."

The 37-year old said no racing event can be compared to F1 but qualified the statement by saying he didn't find it exciting to be in F1 as the cars are not on par with each other.

The series comprising eight rounds, seven in Japan and one in South Korea, will begin on April 13 at Suzuka circuit and conclude at the same place on November 9.

The field includes 24 hour Le Mans winners and WEC World Champions, Andre Lotterer and Loic Duval, former F1 pilots, Vitantonio Liuzzi, Takuma Sato and Kazuki Nakajima, former Force India F1 test driver, James Rossiter, and 2010 Super Formula Champion, João Paulo de Oliveira, who is also Karthikeyan’s teammate at Team Impul, among others.